The present invention relates to a friction clutch operated pressure modulator for anti-locking brake systems for wheel driven vehicles.
For automobiles, motorcycles, and the like, that are provided with an anti-locking brake system, during braking when a given deceleration threshold, for instance 12 m/s.sup.2, is exceeded, an anti-locking device generates an electric signal to reduce the braking pressure until a lower second deceleration threshold, for instance 10 m/s.sup.2, is reached. Now, the anti-locking device generates an electric signal to increase the braking pressure again and deceleration increases up to the first deceleration threshold. This build up and decrease of the brake pressure is effected by means of a pressure modulator.
Such pressure modulators are ordinarily controlled hydraulically by means of separate pumps. Such a construction has the disadvantage that the response time of the pressure modulator is strongly dependent on the viscosity of the hydraulic fluid and on the pressure differential present on it. In addition, it is costly to manufacture and precise regulation is very difficult if not impossible. Furthermore, there is the danger that under unfavorable circumstances failure of the hydraulic pump will result in it no longer being possible for the vehicle to be braked sufficiently, if at all.
Federal Republic of Germany Pat. No. 26 48 042 discloses a magnet-actuated modulator device used to brake a spinning wheel by acting in a manner similar to that of a locking differential. By periodic excitation of the magnet coil, the armature thereof is used to pump hydraulic fluid from a pump chamber into the wheel cylinder of the spinning wheel, thus braking the latter. Such a modulator is not suitable for regulating the braking pressure in an anti-locking device since neither the relief nor the buildup of braking pressure takes place in defined fashion.
For the most part when the prior art has attempted to use electromagnetically operated modulators, the constructions have been unduly large and/or heavy in order to achieve a somewhat linear force/air gap characteristic required to obtain well defined braking characteristics.